Interpretive Summary: Altering the composition of soybean seeds is an important goal for improving the nutritional components of food and feed developed from this important commodity. However, some desired seed composition traits have the potential to vary in degree of the phenotype in ways that preclude efficient development of soybean cultivars. The objective of this work was to determine the variation in carbohydrate profile for soybean seeds with reductions in anti-nutritional carbohydrates. The results of this research demonstrated that seed carbohydrate profile is characteristic depending on the source of the trait, with some phenotypic overlap between lines. Soybean variety selection strategies will have to take into account the impact of the source of the trait as the lines are being developed and phenotyped; the most severe reductions in anti-nutritional carbohydrates should be selected after comparison to appropriate control lines to ensure capture of the major gene and any modifier genes involved in the trait.

Technical Abstract:
Soybeans are an important source of protein-rich meal for livestock feed formulations. Recent changes in the cost of commodity-based sources of metabolizable energy (ME) inputs has put pressure on soybean meal to deliver both protein and ME in feed formulations. The non-oil fraction of soybean contains approximately 12% soluble carbohydrates, principally sucrose, raffinose, and stachyose. Of these carbohydrates, only sucrose is positive for ME. Both raffinose and stachyose, belonging to the raffinose family of oligosaccharides (RFOs) are considered anti-nutritional due to the negative consequences of their fermentation in the gut of monogastric animals when RFOs are consumed in the diet. Therefore, there is an interest in improving soybean seed composition so that it contains higher ME and fewer anti-nutritional components by increasing the sucrose content while lowering the RFOs. Several soybean lines have been discovered that contain altered levels of RFOs, and recent molecular genetic investigations have shown the phenotype to be caused by mutations in a raffinose synthase 2 (RS2) gene encoding the enzyme that is the committed step for RFO biosynthesis. The objective of this research was to determine the variation in carbohydrate profile for different soybean lines grown in a single location containing one of three different alleles of the RS2 gene. The results indicate that although there is variation in the carbohydrate profiles for each line, different lines with the same RS2 genotype tend to produce a characteristic carbohydrate profile.